Editor's note: CNN Contributor Bob Greene is a best-selling author whose 25 books include "Late Edition: A Love Story" and the novel "All Summer Long." He appears on "CNN Newsroom" Sundays during the 5 p.m. ET hour. The opinions expressed in this commentary are solely those of Bob Greene.

(CNN) – CNN Contributor Bob Greene says showing emotion might be a sign of weakness for presidential candidates, but they pay an emotional toll through the campaigns and even worse, a loss.

[0:31] "For the presidential candidates to reveal they are vulnerable to hurt would seem to be an admission of weakness. 'If I'd had feelings,' Richard Nixon told me after leaving the White House, 'I probably wouldn't have even survived.'"

[1:45] "Betty Ford said, of her husband: 'He told us that there always has to be a winner and there always has to be a loser, and that you shouldn't be in politics if you aren't aware of that. We both felt pretty terrible. But we couldn't change it.' Someone will feel that way Tuesday night."